A range finder that transmits laser light to a target object, detects reflected light, and measures a distance to the target object from time difference between transmission time and detection time has been known (for example, see Japanese Patent Application Laid-Open No. 63-244001). Recently, a range finder has been desired to be able to measure a distance of a nearer object.
However, in the conventional range finder, since an optical axis of the transmission optical system and that of the detection optical system are different, when a distance to a target object locating at a nearer distance is to be measured by using a photodetector having the same size as that of the photodetector used in the conventional one, a spot image of the reflected laser light from the target object is formed out of a detecting area of the photodetector disposed in the vicinity of the imaging surface of the detection optical system, so that the distance of a nearer object capable of being measured has a certain limit.